1. Field of the Invention
The present invention relates to a seat slide device suitable for use in an automotive vehicle in which employs at least one pair of guide rails, and specifically to a seat slide device employing an upper slidable guide rail made of light-alloy and firmly secured onto the bottom surface of the automobile seat and a lower stationary guide rail made of light-alloy and rigidly mounted on the floor panel of the vehicle body by means of a leg member, which is capable of adjusting the position of the automobile seat assembly in a direction generally parallel to the longitudinal direction of the vehicle body by varying a relative position of one of the rails to the other through bearings rotatably disposed therebetween.
2. Description of the Prior Art
Recently, there have been proposed and developed various automobile small-sized and light-weight seat slide devices. One such light-weight seat slide device is shown in FIGS. 6 and 7. The light-weight seat slide device is generally comprised of an upper rail 1 made of light-alloy such as aluminum alloy, a lower rail 2 made of light-alloy such as aluminum alloy and bearings 3 made of steel balls disposed between the rails 1 and 2 to permit one of the rails to smoothly move relatively to the other. In general, the respective bearing 3 rotatably moves together with the upper rail 1 by way of a carrier (not shown) attached to the upper rail 1. As clearly seen in FIG. 7, the seat slide rail is traditionally formed with a stopper 2a for restricting a relative displacement of the bearing 3 to the lower rail 2 in one direction thereof. The stopper 2a is formed by cutting out a portion of the upper edge of the side wall at the rear end of the lower rail 2 and by bending the cut-out portion outside of the side wall surface of the rail. The lower rail 2 is rigidly mounted on the floor panel of the vehicle by way of a leg member 4. As shown in FIG. 6, the leg member 4 is fitted to the bottom of the lower rail 2 at the rear end thereof and firmly fixed to the lower rail 2 by means of rivets 5. Alternatively, the leg member may be fixed firmly to the bottom of the lower rail by welding. In the previously-noted prior art seat slide rail device, since the bearing stopper 2a was formed by machining a portion of the lower rail, by way of both cutting-out and bending, undesirable excessive stress would be concentrated at the cut-out and bent section of the lower rail 2. That is, a mechanical strength is remarkably lowered at the cut-out and bent portion of the lower rail 2. For the afore-mentioned reasons, there is a tendency for the lower rail 2 to be deformed at the relatively weaker cut-out and bent section functioning as a bearing stopper. As set forth above, the conventional light-weight slide rail device suffers from the drawback that a smooth sliding movement of the upper rail 1 relative to the lower rail 2 cannot be obtained owing to such deformation at the cut-out stopper of the lower rail.
In the case of excessively large upward break-away load which acts upwardly to break the seat away from the floor panel, e.g. during quick braking, there is a possibility that the lower rail 2 and the floor panel are broken away from each other, because the bottom section of the light-alloy rail 2 has a relatively less rigidity, as compared with the rail mounting member, i.e., the lower-rail mounting leg 4 and in addition a mechanical strength of aluminum alloy is in general inferior to steel. As set forth above, since the mounting strength of the seat slide assembly on the floor panel is dependent on a rigidity of the bottom section of the lower rail onto which the leg member 4 is attached, it is advantageous to enhance a rigidity and a mounting strength of the mounting section of the lower rail 2 on the floor panel.